How much hair do humans have? • On average, each person's head carries about 100,000 hair follicles. Some people have as many as 150,000 or even more.
• On a baby's head, there are about 1,100 follicles per cm square.
• By the age of 25, this number has fallen to about 600, but the number depends on the physical type of the individual.
• Between the ages of 30 and 50, the number drops further, to 250-300. After this point there is only a slight further fall with age.
• Each follicle grows about 20 new hairs in a lifetime. Each new hair grows for several years, and can reach over 1 meter in length.
• Each hair falls out eventually, and is replaced by a new one.
The Hair BulbThe hair bulb lies inside the hair follicle. It is a structure of actively growing cells, which eventually produce the long fine cylinder of a hair.
New cells are produced at a continuous rate in the lower part of the bulb. As they grow and develop they steadily push the previously formed cells upwards. When the cells reach the upper part of the bulb they begin to change, and they form themselves similar to six cylindrical layers, each one inside the other. Consequentially, the inner three layers of cells become the actual hair. The outer three layers become the lining of the hair follicle - the inner root sheath.
The pigment that colors the hair are produced by special cells in the hair. The pigment is called melanin and the cells are known as melanocytes. As the developing hair moves upwards in the follicle, the melanin is carried upwards in the inner part of the hair.